Grammar Answers:
1. The number increased slightly.
2. Attendance decreased significantly.
3. Course sales remained the same.
4. Group A had higher numbers than Group B.

Reading Answers:
1. Group C
2. Group A
3. 8 hours
4. Study hours increased from A → C
5. Each group studied more than the previous one.

Listening Answers:
1. Group A
2. 12 hours
3. Each group studied more
4. Group B studied more